If for some reason, Windows Task Manager starts up whenever you boot up your computer then this is how to remove it.
Download and run Autoruns. You can view all Scheduled Tasks, startup folder applications, msconfig startup entries right from a single convenient view. Look for a startup entry containing taskmgr.exe and delete it. That should fix it.
If Autoruns doesn't reveal anything then you'll want to check out HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon using regedit.exe and delete the entry called Taskman, if it's there. This info came from this particular forum post.